Magnetic core



T. D. GORDY MAGNETIC CORE April 19, 1949.

2 Sheets-Sheet 1 Filed March 17, 1948 Ihventor': Thomas D. GOTd H.

His Attorne s.

T. D. GORDY MAGNETIC CORE April 19, 1949.

2 Sheets-Sheet 2 Filed llarph 17, 194 s Fig.2.

Core Loss-Watts Per Pound Inventor Thomas D.Gor'd g,

'5 Hus Attorne g 'ferro-magnetic material.

Patented Apr. 19, 1949 PATENT OFFICE MAGNETIC CORE Thomas D. Gordy,Plttlfleld, Mass minor to General Electric Company, a corporation of NewYork Application March 1'1, 1948, Serial No. 15,359

2 Claims. 1

This invention relates to magnetic cores and more particularly tolaminated magnetic core structures for use with electrical inductionapparatus such as transformers and reactors.

The laminations for magnetic cores very often are punched or cut fromsheets which are produced by rolling from bars or billets of suitableThe rolling process forms a grain structure in the sheets which normallyextends in the direction in which the sheets have been rolled. It hasbeen found that the path which offers the least resistance to magneticlines of flux through these rolled sheets is parallel to the directionof the grain. Thus, to present a magnetic core having the lowestreluctance and being of a certain specific size it is advantageous toassemble the core sections in such a manner as to allow the magneticflux to follow continuously the line of the grain of the ferro-rnagneticcore laminations.

In the normal lapped core construction it can be seen that the flux mustcut crosswise of the most favorable direction at the ends of thelaminations in traversing from one core leg to the next. Due to thecrosswise flow of flux at the corners of the core relatively high lossesoccur at.

these points. A common way of overcoming the difiiculties referred toabove is to assemble the core laminations, each corner of which has beencut on the diagonal so as toprovide a mitered Joint. It can be seen thatin a core assembled in this fashion the magnetic lines of flux runparallel in all sections of the core to the grain orientation of thelaminations. Thus by the use of mitered joints core losses andexcitation may be decreased.

Besides utilizing, in the construction of a transformer core, a novelmitered lamination arrangement, the laminations are of the split ordivided type. Thus, both the legs and yokes of a core constructed inaccordance with this invention consist of a plurality of paralleladjacent stacked punchings or laminations.

By dividing the laminations the cost of constructing a large core isreduced since the leg and yoke portions can be made from relativelynarrow standard term-magnetic strip widths. And the necessity of using ahighly expensive oversized width stock is negated. Also an improved fluxpath which follows the grain of the core laminations is provided. Afurther advantage of dividing the laminations is the consequentreduction of eddy current losses due to the narrower dimensions of eachlaminar section.

It is an object of this invention to provide a new and improved magneticcore constructed of stacked punched laminations which presents minimumlosses throughout the magnetic circuit.

An object of this invention is to provide a new and improved coreconstruction which is simple to construct, economical to manufacture andefllcient in operation.

A still further object of this invention is to provide a new andimproved split lamination core construction which provides a moreequitable flux density distribution between the inner and outer coresections.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawings and its scope will bepointed out in the appended claims.

In the drawing Fig. 1 is an exploded perspective view of a particularembodiment of the invention. Fig. 2 is a graph illustrating the greaterefliciency of a transformer core constructed in accordance with thisinvention as compared with conventional core constructions. Fig. 3 is apartial front elevation of the particular embodiment of this inventionshown in Fig. 1.

Referring now to the drawing there is shown therein by way of example inFig. l a magnetic core I which has particular application to threephaseelectrical apparatus. The core I consists substantially of threeparallel legs which are each constructed of two adjacent laminar stacksand of four connecting yoke pieces which are also of split construction.The illustrated construction includes one lamination layer 2 having asplit leg I one end of which has a notch t which is parallel to thetransverse axis of the assembled laminations and an edge portion 5 whichis parallel but offset from an adjacent diagonal running from the corner6 to the outside corner I of the assembled lamination layer 2. Acooperating outer split yoke sheet I has a straight or extending portionI, which corresponds to the notch 4 of the split leg 3, and a secondportion lti which cooperates with the diagonal edge 5 of the split legsheet 3. Similarly a split yoke sheet II is provided which is anequivalent to the yoke sheet 8 and includes a notched portion l2, whichcooperates with a notch portion ii of the split outer leg sheet 3, bothof which are parallel to the transverse axis of the assembledlaminations. The remainder of the mitered butt Joint is provided by asurface ll of the lamination It and a surface ii of the lamination 8both of which surfaces are parallel and offset from a diagonal runningbetween the inner corner it and the outer corner lta of the assembledlaminations. The remaining outer sembled laminations. An edge portion28" of .the

leg sheet II mates with a corresponding edge of the yoke sheet 28, bothof these portions are parallel and oifset from a diagonal running from A.Eg'. similar edge 28 of the leg sheet ll cooperates with a portion 29of the yoke sheet 23. and the an inside corner 28 to an outside corner27.

butt joint thus presented is parallel and ofiset from a diagonal runningfrom an inside corner 38 to an outside corner 3|.

The other extremityof the yoke sheet 23 is provided with amating edgesurface portion 32 which is parallel'to the longitudinal axis and asecond portion 33 which runs diagonally from the edge portion 32 at anysuitable angle. Similarly the otherend of the yoke sheet 28 is providedwith an edge portion 34 which is parallel to the longitudinal axis 'ofthe assembled lamination and a second edge portion 35 which runsdiagonally from the edge portion 34 at any suitable angle. Cooperatingwith the edges of the yoke sheets-8, II, 28 and 23 there is provided acentral leg sheet 38 having -extended portions 31 and 38 which mate withnotches 32 and 34 of yoke sheets 23 and 28 respectively and havingdiagonals 39 and 48 which cooperate with a portion of the diagonals 33and 350i the yoke sheets 23 and 28 respectively. The remainder of thediagonals 33 cooperates with a corresponding diaonal 4| of the'yokesheet I I, and the remainder of the diagonal 35 corresponds with thediagonal 42 of the yoke sheet 8. The central leg sheet 38 is edge 11 ofthe outer leg sheet 3; the remainder of the edge I'I cooperates with thelongitudinal edge I8 of the inner leg sheet 5i. The transverse edges '79and 88 of the inner yoke sheets 58 and 89 cooperate with the transverseedg es 8i and 82 of the outer yoke sheets 8 and II. The inner leg sheet83 has extended portions 88 and 85 which are parallel to thelongitudinal axis of the assembled laminations and cooperate with thenotches 88 and 87 of the inner yoke sheets 88 and "'89. The offsetdiagonal edges 98 and 9I of the vinner leg sheet 83 cooperate withcorresponding offset diagonal edges 92 and 93 of the inner yoke sheets88 and 89 and the transverse edges 94 and "85 of the inner leg sheet 83cooperate with part of the edges 96 and 97 of the outer yoke sheets 28and 23. The remainder of the edges 98 and 97 contacts the edges 98 and99 of the inner yoke sheets 88 and 89 respectively. The longitudinaledge I88 of the inner leg sheet 83 cooperates with the correspondingedge I81 of the outer leg sheet IT. The longitudinal edges I82 and I83of the inner yoke sheets 88 and 89 butt up against the longitudinal edgeI84 of the central leg sheet. '-It can be seen from Figs. 1 and 3 thatlamination layer I85, which is contiguous to lamination layer 2, isidentical in form with lamination layer 2 except it has been flippedover or rotated 180 about its longitudinal axis. Thus, the adjacentjoints between contiguous laminations will be on opposite sides of theadjacent diagonal running between corresponding inside and outsidecorners of the assembled laminations. Therefore;

. the possibility of gaps being formed at the joints provided with twonotched portions 43 and 44 which correspond to the extended portions 45and 48 of the yoke sheets I I and 8 respectively. These portions areparallel to the transverse axis of the assembled laminations. A suitablediagonal 41 of the yoke sheet II corresponds with a similar diagonal 48of the central leg sheet 38 and a similar diagonal 49 of the yoke sheet8 cooperates with a corresponding diagonal 58 of the central leg sheet38. p The inner core sections comprise a'leg sheet 5I having notches 52and 53 which are parallel to the transverse axis of the assembledlaminations and offset diagonals 54 and 55. The inner yoke sheet 58 hasan extended portion 5'I'which corresponds with the notch' 53 of theinner leg sheet 5| and an offset diagonal 58 which corresponds with theoffset diagonal 55. The inner yoke sheet 59 similarly has an extendedportion 88 which corresponds to the notch 52 and an offset diagonal 8|which cooperates with the diagonal 54 of the inner leg sheet 5|. Theremaining extremities of the inner yoke legs 58 'and 59 have extendedportions 82 and 83 respectively which cooperate with the notchedportions 84 and 85 of the central leg sheet 88. Also the yoke sheets 58and 59 have diagonal portions 81 and 88 which cooperate withcorresponding diagonals 88 and I8 of the central leg sheet 88. The yokesheets 58 and 59 have portions II and 12 which are parallel to thelongitudinal axis of the assembled laminations and cooperate with partof edge13 of the central leg sheet 38; the remaining portion of the edge13 contacts the edge I4 of the central leg sheet 88. It can also be seenthat the longitudinal edges 'I5'..and I8 of the inner yoke sheets 58 and59. cooperate with part oft'the and the consequent increase of magneticreluctance is substantially eliminated. Examining the layer 2 as shownin Fig. 1 it can be seen that flux flowing in the inner core path mustflow crosswise across the grain of more 40 favorable magnetic reluctancein passing from the inner yoke sheets 88 and 89 to the central leg sheet36.. Normally there is a tendency for the flux to concentrate itself toa greater extent inthe inner core section but since it must travelacross the grain of the central leg sheet 38 in passing to the inneryoke sheets 88 and 89 the reluctance of the inner magnetic path isiricreased and a more favorable distribution of flux is achieved.

Fig. 2 illustrates a comparison between the magnetic characteristics ofa core constructed in accordance with this invention and comparable'cores constructed one as a split lapped core and the other merely as alapped core. In Fig. 2 there is plotted as the abscissa of a graph thecore losses inwatts per pound with flux density being represented on theordinate axis. Curve I 88 represents the watts loss per pound for aparticular core constructed in accordance with this invention, curve INthe watts loss per pound for a similar split lapped core, and curve I88the watts loss per pound for a similar lapped core, It can be seen fromFig. 2 that the core constructed in accordance with this invention, thesplit-lapped core, offers the highest degree of efi iciency. I

While there has been shown and described a particular embodiment of thisinvention it will be obvious to those skilled in the art that variouschanges and modifications "can be made therein without departing fromthe invention and, therefore, it is aimed in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the-invention.

What I claim as new and desire to secure as Letters Patent of the UnitedStates is:

l. A unitary magnetic core for three phase electric induction apparatuscomprising, in combination, a plurality of flat stacked rectangularoutline lamination layers each comprising three straight parallelwinding legs whose ends are joined by separate straight yokes, the twoouter legs and the yokes of each layer being divided longitudinally intoinner and outer straight parallel lamination pieces with the width ofcorrespondingly located pieces the same in all layers so that the twoouter core legs as a whole and the core yokes as a whole are effectivelylongitudinally split into inner and outer parts which are separated by alongitudinal gap across which flux can pass only with difliculty, thecenter leg of each layer being divided longitudinally into two straightparallel lamination pieces with the width of correspondingly locatedpieces alternately relatively wide and relatively narrow in successivelayers so that the center core leg as a whole is effectively solid andhas a longitudinal lapped REFERENCES CITED The following references areof record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,891,178 Porter Dec. 13, 19322,407,626 Welch, Jr Sept. 17, 1946

